mmobder kdbx itself is just a file and doesn't offer any special countermeasures. It's a static file.
Concerning opening the file it the only portable (between systems) ways I see are password+static file. I don't think the actual U2F works, just a static key as a master password .
OTP from the yubikey /similar can be used as well, but I don't think it can be used as 2fa? Does any of these providers work on Linux (keepassxc?) or android?
HMAC challenge/response could be used, but it can't, because Keepass 2 and KeePassXC use different implementations.
Keepass2Android also seems different and to make things worse it enforces synchronising the database, or OTP will stop working. Worst of both worlds.
If not then the password manager than can only be used on one platform isn't so convenient or useful.
So yeah, static password + static key file OR static password on yubikey . Other options not so much, unless all three manuals are wrong.